1. Field of the Invention
The present invention relates to a clean bench used to sort polycrystalline silicon according to size or quality, which is used as a raw material to be melted in producing single crystal silicon, and a method of producing a raw material for single crystal silicon including a process for cleaning the polycrystalline silicon.
2. Description of the Related Art
Generally, in producing polycrystalline silicon for use as a raw material of single crystal silicon, a heated silicon seed rod is exposed to raw gas including chlorosilane gas and hydrogen gas. Polycrystalline silicon is deposited in a cylindrical shape from the silicon seed rod, and crushed into lumps with proper size or cut into rods with a predetermined length, thereby providing a raw material for single crystal silicon. The polycrystalline silicon, a raw material for single crystal silicon, is packed and sent to a single crystal silicon producing factory. Before packing, the polycrystalline silicon is manually sorted according to size or quality. Such a sorting process is carried out, for example, in a clean bench, as illustrated in Japanese Unexamined Patent Application, First Publication No. 2005-279576. The clean bench includes a blower to supply air to a working space formed on a worktable through an air supplying high-performance filter and an suction hole to suction air from the working space. The working space is continually supplied with clean air through the blower and the suction hole, so that cleanliness on the worktable is kept highly. Accordingly, when polycrystalline silicon is sorted, this process prevents impurities from adhering to the polycrystalline silicon and particle of polycrystalline silicon itself is removed by the flow of clean air. As a result, the quality of single crystal silicon to be produced can be improved.
By the way, when sorting by size or quality of polycrystalline silicon is conducted in a clean bench, if particles are charged, the particle electrostatically adheres to the polycrystalline silicon. Thus, the particle cannot be removed by the flow of clean air. The required removal effect can not be achieved.
Therefore, it is an object of the present invention to provide a clean bench which is capable of preventing particle from adhering to polycrystalline silicon to maintain the quality of single crystal silicon to be produced, the clean bench being used to sort the polycrystalline silicon according to size and quality, and a method for producing a raw material of single crystal silicon.